A double-headed swash plate type compressor applied to an automobile air conditioning system, for example, has a drive shaft, a pair of cylinder blocks supporting the drive shaft for rotation, and a swash plate fixedly supported on the drive shaft for rotation together with the drive shaft in a swash plate chamber formed in a region including the boundary between the pair of cylinder blocks. A plurality of cylinder bores are formed so as to extend in both the cylinder blocks and are arranged around the drive shaft. Double-headed pistons are fitted for axial movement in the cylinder bores, respectively. Each piston is operatively engaged with the swash plate via shoe elements. The rotary motion of the swash plate is converted into the linear motion of the pistons for the suction, compression and discharge of a refrigerant gas.
A single-headed swash plate type compressor has a cylinder block, and a housing closing an inner end of the cylinder block and having a swash plate chamber or a crank chamber. A swash plate is mounted on a drive shaft in the swash plate chamber and is engaged with pistons by shoes. Further, in a variable-displacement swash plate type compressor, a swash plate is engaged with single-headed pistons fitted in a plurality of cylinder bores by shoes, and is mounted on a drive shaft so as to wobble on a supporting point. The inclination of the swash plate is changed according to pressure in the crank chamber so that gas pressures acting on the opposite ends of the single-headed piston balance each other. Consequently, the stroke of the single-headed piston is adjusted to control the displacement of the compressor.
The demand for weight reduction in the aforementioned swash plate type compressors has progressively increased and the swash plate type compressors for automobile air conditioning or climate control systems, including the swash plates, the pistons, and the cylinder blocks are now made of aluminum alloys. Therefore, abrasion-resistant and seizing-preventive measures have been examined to protect surfaces exposed to severe, high-speed abrasive actions for a long time, such as the surfaces of the swash plate in sliding contact with the shoes, and the sliding contact surface of the piston in sliding contact with the surface of the bore. Such measures include the formation of a fluorocarbon resin film on the sliding contact surface of the piston and the formation of a film of a solid lubricant on the sliding contact surface of the swash plate.
The double-headed piston, however, is provided with a recess extending across the periphery of the swash plate, and interfering surfaces formed in the recess to prevent the piston from rotation about its own axis come into impulsive contact with the outer circumference of the swash plate to prevent the piston from rotation by a rotation moment acting on the piston. The single-headed piston is provided with a rotation-preventive interfering surface in its base end part, and the interfering surface comes into impulsive contact with the inner surface of the housing to restrain the piston from rotation. Accordingly, it is possible, under a substantially nonlubricated state which occurs at the start of the compressor, that seizing occurs between the interfering surface of the piston and the outer circumference of the swash plate, and attempts have been made to form a lubricating film over the interfering surface of the piston and the outer circumference of the swash plate. However, in formtion of a lubricating film, when, for example, a spray coating process for coating the swash plate with a lubricating film is used, the yield of formation of the coating material film is usually very low. Furthermore, since the strength of an adhesive bond of the lubricating film and the sliding contact surface is low, such a protective measure using the lubricating film is not satisfactory in reliability as well as in its seizing-preventive effect.
It is an object of the present invention to provide an improved swash plate type compressor capable of providing improved functional reliability attained by employing an improved swash plate coated with an excellent film and capable of being manufactured with a high productivity.
Another object of the present invention is to provide a long-life swash plate type compressor capable of properly functioning, over an extended period of use, when applied to an automobile air conditioning system and driven by the engine of a vehicle to compress a refrigerant.
In accordance with the present invention, there is provided a swash plate type compressor which comprises: a cylinder block provided with a plurality of cylinder bores; pistons fitted in the cylinder bores; a drive shaft supported for rotation about its axis of rotation; and a swash plate supported for rotation together with the drive shaft, having at least sliding contact surfaces to be in sliding contact with shoes and operatively engaged with the pistons via the shoes; wherein the sliding contact surfaces of the swash plate in sliding contact with the shoes are coated with a film of at least one solid lubricant selected from molybdenum disulfide, tungsten disulfide and graphite by a transfer method.
The film of the solid lubricant formed on the sliding contact surface of the swash plate in sliding contact with the shoes exercises excellent lubricating performance, and the transfer method of forming the film of the solid lubricant is very advantageous from the viewpoint of economy and productivity in the yield of the coating material and the control of the thickness of the film.
If the swash plate has an outer circumference to be in impulsive contact with interfering surfaces formed respectively in the pistons, it is preferable that a film of the solid lubricant is formed on the outer circumference by a transfer method. Thus, the contact surface to be in impulsive contact with the piston, in addition to the sliding contact surface in sliding contact with the shoes, is able to secure a further satisfactory seizing-resistant property.
If the sliding contact surfaces of the swash plate on which the film is formed, i.e., base surfaces for the film, are subjected to a surface roughening process, a coating material for forming the film is forced to dig into minute irregularities formed by the plastic deformation of the base surfaces to provide an anchoring effect which enhances the strength of connection of the film to the base surfaces. If the sliding contact surface and the outer circumference of the swash plate are coated for surface preparation with a plated film of a material containing tin as a principal component, the plated film prevents the aluminum base of the swash plate from being exposed even if part of the plated film falls off, and serves as a lubricating layer. Therefore, the swash plate has excellent durability.
Preferably, the film formed on the sliding contact surface of the swash plate is finished by grinding to adjust the thickness of the film and finish the surface of the film in a high surface accuracy (flatness).